Ammonia (NH3) is an atmospheric pollutant mainly emitted by the agricultural sector. It is a precursor of fine particles (PM2.5) and therefore has a major effect on public health, and climate change. The volatilization process of NH3 and its lifetime in the atmosphere, as well as its transformation into particles, are poorly constrained and strongly depend on meteorological parameters, in particular temperature. Although current satellite measurements have evaluated NH3 spatio-temporal variabilities at various scales (global, regional, and local), observations of NH3 diurnal variability and their diurnal variability and dependence to temperature are poorly constrained. This strongly influences our ability to correctly simulate NH3 emissions and associated particulate pollution events in atmospheric models. The IRS (InfraRed Sounder) instrument which will be launched on the MTG (Meteosat Third Generation) satellite into geostationary orbit in late 2024, will offer the ability to deepen this analysis with more frequent measurements (every 30-45 minutes over Europe and Africa) and better spatially resolved observations (4 km x 4 km at the Equator). In this presentation, we show the potential of the new geostationary IRS-MTG mission to assess spatio-temporal variabilities of ammonia and temperature focusing on a case study over the high NH3 emitted region of Brittany (France). Using atmospheric states simulated using the CHIMERE chemistry-transport model at the effective spatial resolution of IRS over Brittany, synthetic spectra are computed using the 4A/OP radiative transfer model. NH3 measurement-sensitivity of the future IRS-MTG mission is discussed with regards to the presently available IASI observations.